The bromodomain (BRD) and extra terminal domain (BET) family of proteins, which function as 'readers' of histone acetylation marks, mediate growth of pancreatic ductal adenocarcinoma (PDAC) cells in 3D collagen. Additionally, PDAC cells in 3D collagen demonstrate chemoresistance through increased expression of high mobility group A2 (HMGA2), an architectural protein that regulates chromatin structure. The long-term goal is to help develop novel mechanism-based targeted therapies for the treatment of PDAC. The objective in this application is to determine how BET proteins mediate chemoresistance and contribute to fibrosis in vivo. The central hypothesis is that BET protein inhibition will decrease PDAC tumor growth and increase chemosensitivity by decreasing the cancer stem cell population and HMGA2 protein function, respectively. A second hypothesis is that BET inhibition will lead to an attenuation of fibrosis in PDAC tumors. These hypotheses are based on strong preliminary data demonstrating that BET inhibitors decrease growth of PDAC and stellate cells in 3D collagen. In addition, treatment of PDAC cells with BET inhibitors decreases cancer stem cell population and represses HMGA2. The rationale is that a determination of the role and underlying mechanism of BET proteins in PDAC progression in vivo is likely to contribute substantively to a conceptual framework whereby new clinically effective targeted therapies can ultimately be developed. Three specific aims are proposed: 1) Determine the role of BET proteins in PDAC progression in vivo; 2) Evaluate the ability of BET protein inhibition to increase chemotherapy sensitivity; and 3) Evaluate the ability of BET protein inhibition to attenuate fibrosis. Under the first aim, the effect of BET inhibitors on PDAC progression will be determined in mouse models. Further, the extent to which BET inhibitors decrease PDAC stem cell population in vivo will be evaluated. Also, the ability of gold nanoparticles (Au-NPs) coupled with BRD4 siRNA to inhibit tumor growth will be determined. For the second aim, the ability of BET inhibitors to increase chemotherapy efficacy will be evaluated in 3D collagen and in mouse models. Additionally, the role of BET proteins in DNA damage response and the contribution of HMGA2 to BET protein regulation of chemoresistance will be assessed. In the third aim, the mechanism by which BET inhibitors regulate stellate cell activation and collagen production will be determined. The effectiveness of BET inhibitors and Au-NPs functionalized with BRD4 siRNA to attenuate fibrosis in mouse models will also be evaluated. The research proposed is innovative because it utilizes complex models of pancreatic cancer, including in vitro organotypic cultures and in vivo orthotopic and transgenic mouse models to determine the role of BET proteins in PDAC progression. An additional innovation is the use of Au-NPs functionalized with siRNAs to downregulate BRD4 expression in the model systems. This proposed research is significant because it is expected to provide strong scientific justification for the continued development and future clinical trials of BET inhibitors in PDAC.